The present invention pertains in general to monitoring and charging operations for batteries and, more particularly, to the charging and monitoring operations of a battery that is utilized to power a microprocessor based system.
With the advent of small portable computers, commonly referred to as laptop computers, the need has arisen for a reliable power source that can both operate independent of an external supply and for relatively long durations of time. With present portable computers, it is desirable to have a battery powered system operate reliably for the duration of use, which could be an airplane flight, a business meeting, a conference, etc. This use could extend to as long as three hours. Typically, the manufacturers of battery systems or battery packs for the portable computer market specify the duration of time that a xe2x80x9cfully chargedxe2x80x9d battery pack will operate a given computer. However, this necessitates that the battery pack is in good working condition and that it is fully charged. If the computer had been utilized for an unknown amount of time prior to going into the meeting or traveling on an airplane, the user would have no idea as to what the capacity of the battery is. As a result, users typically carry backup battery packs and try to maintain their battery packs at a fully charged condition by charging them prior to their meeting or their airplane trip.
In order to provide information as to the status of the given battery, it is necessary to get some idea of the amount of charge stored in the battery. There have been a number of systems proposed in the past to provide xe2x80x9csmartxe2x80x9d charging systems that can determine the capacities and the efficiencies of the batteries. One such system is disclosed in U.S. Pat. No. 4,918,368, issued Apr. 17, 1990. The ""368 Patent discloses a battery charging system that is controlled by a microprocessor to charge and discharge batteries while periodically affecting the monitoring and control operations in which battery current data is registered to accumulate capacity data relative to that battery. The disadvantage to this type of system is that it requires a dedicated microprocessor to control all the functions that are provided by the system, which functions are known features for monitoring and controlling charging of the battery. Some of these functions are described in U.S. Pat. No. 3,876,921, issued Apr. 8, 1975, U.S. Pat. No. 4,746,852, issued May 24, 1988, and U.S. Pat. No. 3,617,851, issued Nov. 2, 1971. Each of these patents discloses various methods for charging the battery and also for monitoring the capacity thereof.
Typically, the capacity of a battery can only be determined by fully discharging the battery after charging it up to full charge. Therefore, any monitoring and charging circuit must be capable of performing this operation. If a new battery is put into a system, its charge state cannot immediately be assessed, but, rather, some analysis of the battery must be performed to determine its charge status. Typically, batteries have been tested at the factory and then are fully charged by the user prior to putting them in the system. Some charging circuitry may be utilized with a given system, such as that described above in the ""368 Patent, to provide some control over the charging operation while the battery is in the system. However, monitoring operations that are performed by the system take valuable time of the microprocessor and must be a function of the microprocessor. No systems presently provide a totally integrated function to provide full monitoring and charging control for a battery supply in a portable computer.
The present invention disclosed and claimed herein comprises a method for determining the charge state of a battery that is utilized by a system, which system during operation thereof comprises a system load. The system is operated with the battery such that the battery load comprises the system load. The amount of charge removed from the battery is first determined while under the system load and also while the battery is discharging. This determining step is initiated when the battery is at a first charge level. The determining step is terminated when the battery charge level reaches a second charge level that is below the first charge level. Thereafter, the capacity of the battery is calculated as the amount of charge removed from the battery between the first charge level and the second charge level.
I another aspect of the present invention, the determining step is initiated whenever it is determined that the battery is at a substantially full charge level and, thereafter, the discharge operation is initiated. Similarly, the termination operation of the determining step occurs when the battery voltage falls below a predetermined end-of-discharge voltage level.